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Dirty Boats

Cleaning up the dirtiest mode of transport is hard, but worth it.

You were probably expecting some snarky, humor-filled blog post addressing the heedless attack of the judiciary on the EPA’s ability to fight climate change from power plant gunk, but for that I will refer you to brilliant legal minds commenting here, here and here. I am in a deep funk about our prospects to do something meaningful to save our butts, so I did what I do when I need to snap out of it: read some cool new papers and decided to tell you about one I loved. 


Did you know that maritime ship traffic (think boats bringing your 75’’ TV from Asia to SF) emits as much as half of all the fine particulate matter (=the bad stuff) from global road traffic? Did you know that these big boats along the US coastline are allowed to use fuel that has 3,500 times (!!!) the sulfur content than that allowed in vehicles? This is of course bad news for folks living near ports, but what I did not know is that these dirty vessels are responsible for 20% of sulfur dioxide emissions on the west coast and a whopping 38% on the East Coast! I learned these facts from a cool new paper by my UC Davis colleague Jamie Hansen-Lewis and her coauthor Michelle Marcus

They point out that efficiently regulating emissions from ships is really tricky. If you have many moving sources of pollution (boats) and many receptors (humans, plants, soils and lakes) things get challenging – especially when the air quality chemistry is complicated and transport of the pollutant is influenced by wind, sun and precipitation. To further complicate this regulatory calculation, the air pollution emitted by ships does more than pollute the air.   These aerosol emissions have a cooling effect on the surface, in many places offsetting the effects of global warming. In some areas this reduced warming can be a good thing, while for others (like agriculture) there is complicated chemistry involving raindrop and cloud formation resulting in a double whammy bad thing. One hypothesis is that you really want to reduce pollution near shore to reduce negative health effects in coastal populations, but maybe not so much on the open ocean to offset some of the warming (although I am not sold on the latter). 

The paper examines the first regulation of maritime pollution, called emission control areas (ECAs) imposed in 2012. This regulation required all commercial ships to use low sulfur fuel within 200 miles of the US coast. Alternative options were to install abatement equipment or pay fines. In 2020 the International Maritime Organization imposed similar standards globally, at an estimated cost to shippers of US$10-60 billion globally. These are not peanuts, or “seanuts” in terms of costs. Hansen-Lewis and Marcus decided to check whether the policy actually worked. 

The econometric identification strategy is clever and as good as you are going to get in this tricky empirical setting. The data work is first rate as well. They find that the policy led to a “4 percent decrease in the population-weighted average fine particulate matter across U.S. counties within 200km of heavy ship traffic”. That is not peanuts either. Employing a true “fate and transport” model that properly figures out how pollution forms and travels (instead of being lazy like the rest of us and using distance), they find that the policy results in a 1.7 percent average reduction in the incidence of low birth weight and a 3.5 percent decline in infant mortality. 

But Max, how does this compare to the cost of the policy for those poor shippers? Turns out the infant health results alone equal 90% of the annual costs of the policy. Add to this the effects on old people like me or exercise nuts like Meredith and you easily get a benefit-cost ratio exceeding one. So in short, the policy worked! 

What else did we learn from this paper? Here at the Energy Institute we have long harped on the fact that ex-ante estimated benefits from future regulations often drastically overestimate the benefits from proposed regulation (how much weight you hope to lose after the holidays is usually a bigger number than the weight loss realized by, say, March). As a species, we spend way more time telling stories about the anticipated effects of future regulations instead of checking ex-post (fancy Latin for looking the rearview mirror) whether they worked. I was part of a team with people way cooler than me, doing a survey of this for the Clean Air Act. 

In this same spirit, the paper by Hansen-Lewis and Marcus does a lovely comparison for this policy and finds that the ex-post realized benefits are much smaller than the ex-ante predicted benefits. They show credible evidence for why this is. First off, boats changed their routes to avoid being subject to the policy. Second, they show evidence that improvements were smaller in counties with better air quality (far from the NAAQS from the Clean Air Act). Third, individuals spent more time outside after the policy and were still subject to air pollution from other sources. 

In sum, this is a beautifully executed paper that makes a number of important steps forward in the literature on policy evaluation. However, I note that this sector is severely understudied and that future work would be particularly valuable. I also recommend you read this paper and if you enjoy it as much as I did, send the authors a note sharing your appreciation! The ratio of (nasty referee reports + Twitter snark) over nice random notes from readers is a number much greater than one!

Keep up with Energy Institute blog posts, research, and events on Twitter @energyathaas.

Suggested citation: Auffhammer, Maximilian. “Dirty Boats”  Energy Institute Blog, UC Berkeley, July 5,  2022,

Maximilian Auffhammer View All

Maximilian Auffhammer is the George Pardee Professor of International Sustainable Development at the University of California Berkeley. His fields of expertise are environmental and energy economics, with a specific focus on the impacts and regulation of climate change and air pollution.

10 thoughts on “Dirty Boats Leave a comment

  1. A very interesting article on an oft-overlooked issue. However, decarbonizing merchant shipping probably implies switching to hydrogen. The safety and security implications of merchant ships laden with large amounts of such a highly explosive fuel are significant and may well be a show-stopper:

  2. Adding the emissions and congestion from truck traffic at ports and that 75″ TV looks pretty hazardous. Luckily though, an 85″ wouldn’t be too much worse.

  3. We may not get all the ships to comply to these standards under their own power, but what if we required all shipping coming into our bay waters be pulled and pushed by Electric battery powered tugboats? Even the harbor pilot boat could be electric powered. We use bridge tolls to pay for BART, Ferries and Busses so why not use tolls and ship birthing fees available for electric tugboats? In fact, all the money the district is saving on no longer paying toll takers to grab our money, let Fast-Trak pay from all the tolls they take.

  4. Max, we can agonize over details of this-or-that carbon pricing policy, and how it might be enforced; how emission control areas might be re-defined; we can ponder moving sources of pollution, receptors, complicated air quality chemistry, and how pollutants are influenced by wind, sun and precipitation; we can propose other band-aid solutions to a problem expected to produce 17% of all global GHG emissions by 2050.

    Or, we can stop wasting time and move forward with its only truly viable solution; one that will predictably produce 0% of sulfur dioxide emissions on both east and west coasts; one with a virtually endless supply of fuel and a spotless record of safety; one proven in practice to not reduce carbon emissions, but eliminate them entirely:

    “The US Navy has accumulated over 6200 reactor-years of accident-free experience involving 526 nuclear reactor cores over the course of 240 million kilometres, without a single radiological incident, over a period of more than 50 years. It operated 81 nuclear-powered ships (11 aircraft carriers, 70 submarines) with 92 reactors in 2017. There were 10 Nimitz-class carriers in service, each designed for 50-year service life with one mid-life refuelling and complex overhaul of their two A4W Westinghouse reactors.”

    Commercial nuclear shipping is inevitable. When the only major hurdle to overcome is exaggerated fears about safety, why make an already difficult problem more difficult than it needs to be?

    • Panama and Liberia have the two largest registries of the merchant fleet. Putting nuclear powered ships under the flags of those nations is a non starter. The small number of navies with nuclear powered ships have much higher security arrangements than exist in the merchant fleet. What will pirates in Somalia due with a nuclear tanker?

  5. The problem of particulate air pollution from ships might largely be solved by using zero net carbon biofuel. In the short term this might be the only practical solution to both the problems of carbon dioxide production and other air pollution from ships, as biofuel can be used in existing diesel engines with relatively minor modifications. This is of course if enough carbon neutral biofuel can be made for both shipping and airliners. See:

  6. “Third, individuals spent more time outside after the policy and were still subject to air pollution from other sources. ”

    What’s the explanation for this? If it’s caused by the regulation (which may be a reach), then it’s a benefit that should be measured along with the health effects. If it’s unrelated, then it’s also likely impossible to anticipate, so it should be treated differently in a comparison of ex ante vs ex post results.

  7. It is well known that maritime ship traffic emits a significant amount of particulate matter and uses bunker oil fuel. The paper was informative Albeit probably for a different blog, the blog article itself could have been more helpful by discussing best available control technology, the funding available to install the control technology, commercialization, and examples of success stories, and future technologies such as flow redox batteries. Please see three article here for examples –

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